The invention described herein may used by or for the Government of the United States of America without the payment of any royalties therefor.
A Computer Program Listing Appendix is hereby expressly incorporated by reference. The Computer Program Listing Appendix includes two duplicate compact discs. The files on each compact disc, their size in bytes, and the date created are:
The invention is a software based model for the design and assessment of laser eye protection and in particular interference filter type laser eye protection.
Interference based filter technology has been under development in all branches of the Department of Defense since the 1980s. By creating square or sinusoidal gratings in a material layer through either controlled exposure to mutually interfering laser beams in appropriate photographic media or by depositing multiple layers of material with alternating refractive indices, light rays whose wavelength is the same as the path length between the refractive interfaces are preferentially reflected rather than transmitted.
There are basically three different manufacturing processes under development to produce the requisite interference layers to provide adequate laser eye protection. All three technologies reject narrow xe2x80x9cnotchesxe2x80x9d of the spectrum by design. The peak wavelength rejected (i.e. the exact spectral location) is dependent upon the fringe spacing and incident angle of the impinging radiation with respect to the fringe gradient (i.e. the direction perpendicular to the plane of refractive index fringes at any location). This requires that the filter be carefully designed to reject anticipated incident wavelengths at angles determined by the relative location of the eye behind the laser eye protection (LEP) surface over the range of possible incidence angles.
Prior to the present invention, the inventors were aware of only one other attempt at a similar effort to overlay either predicted or measured angular rejection performance with precise geometric rejection requirements for any eye of a given description and location behind the LEP surface. That effort was solely designed to describe holographic visors and model their predicted performance against eye requirements in Visual Basic.
The primary object of the present invention is to provide an accurate, data-based, three-dimensional representation (graphical) of the protection provided by reflective (i.e., dielectric stacks, holograms, or rugates) or hybrid filters (combination of interference technologies or interference filters and absorptive dyes). The preferred embodiment focuses on modeling the Navy""s hybrid spectacles and visors. However, the novel aspects and advantages described herein are applicable to any reflective filter or barrier material.
One aspect of the invention is to assess the effectiveness of an existing LEP device, such as a visor or a pair of spectacles. Another aspect of the invention is to develop, evaluate, or modify a proposed filter design.
The present invention generates a graphical three-dimensional representation in real time of the complex geometry of interference filters. The three-dimensional graphic and assessment features permit the user to completely model the protection for any desired choice or combination of eye parameters or incident laser direction. The invention displays protection based on the actual optical density recorded across a number of locations on an actual filter surface over a range of incident angles. These features are combined with real time response to user inputs through a graphical user interface (GUI) resulting in a powerful new tool for assessing the degree of protection provided by interference based laser eye protection.
The risk assessment features of the invention allow the user to quickly see which portions of the interference filter fail to protect the retina and more specifically the user defined areas around the central fovea. The ability to view which eye and laser incidence angles produce hazards in user defined regions of the retina is an important feature. With this feature, the user can weigh the likelihood of injury against other important aspects of the filter such as overall transmittance (i.e. visibility through the LEP device) or transmittance of key phosphors or displays.
The invention provides a method of assessing the effectiveness of a laser eye protection (LEP) device having an interference filter surface (IFS), comprising (A) specifying optical densities at a number of points on the IFS for a user specified range of incident angles of a given wavelength of laser light at each of the number of points; (B) entering the specified optical densities into a computer; (C) entering properties of the IFS into the computer; (D) entering properties of an eye into the computer; (E) entering properties of the given wavelength of laser radiation into points on the computer; (F) defining a grid using for the IFS and assigning values of optical densities to points to different optical densities, respectively; (H) generating and displaying a three-dimensional image of the eye and IFS using a graphical user interface (GUI), (I) using the GUI, selecting an incident angle orientation for the given wavelength of laser light and coloring the IFS as a function of optical density on the IFS; (J) using the GUI, selecting an eye orientation and projecting a pupil surface onto the IFS at a point of interest along the incident angle selected in step (I); and (K) determining an average optical density for that portion of the IFS intersected by the projected pupil surface of step (J) and coloring the portion in accordance with the determined average optical density.
In one aspect of the invention, the specified optical densities of step (A) are obtained by providing an LEP device, exposing the LEP device to the given laser wavelength and measuring optical densities at the number of points on the IFS for the user specified range of incident angles at each of the number of points.
In one embodiment, the IFS has a spherical shape and the properties in step (C) include a radius of curvature, a face form angle, a pantoscopic tilt, a substrate transparency, and a location of an optical center of the IFS; and the properties in step (D) include an eye location, a pupil diameter and an amount of eye rotation.
In another embodiment, the IFS has a toroidal shape and the properties in step (C) include two radii of curvature, a pantoscopic tilt, a substrate transparency, and a location of an optical center of the IFS; and the properties in step (D) include an eye location, a pupil diameter, an amount of eye rotation and an interpupillary distance.
The invention further includes, (L) selecting a second grid on the IFS, and, for each grid point on the second grid and for eye orientations generated by rotating the eye, projecting a pupil surface onto the IFS at said each grid point and calculating the maximum incident angle at which the given wavelength of laser light may enter the pupil at said each grid point; and displaying in tabular form the location of said each grid point and its respective maximum incident angle.
In one embodiment, the IFS has a spherical shape and the calculating in step (L) is limited such that the maximum incident angle at which the given wavelength of laser light may enter the pupil at said each grid point is found in a plane defined by an eye center point, a center of curvature of the IFS and each grid point, respectively.
Another aspect of the invention is, (M) selecting a grid point and its maximum incident angle from step (L) and displaying on the GUI a three-dimensional image of the eye and incidence angles of laser radiation corresponding to the maximum incident angle for that grid point. The invention further comprises displaying numerically the eye orientation and laser light incident angle orientation corresponding to the maximum incident angle for that grid point.
Yet another feature of the invention is, (N) using the GUI, selecting a single maximum incident angle for the given wavelength of laser light for all grid points and coloring the IFS as a function of optical density on the IFS.
The invention further includes, (O) for the eye and incidence angles of laser radiation from step (M), displaying on the GUI a three-dimensional image of only those eye and laser light incident angle orientations that will result in laser light striking the fovea critical region or the fovea caution region.
Still another aspect of the invention is, (P) for the eye and incident angles of laser radiation from step (M), displaying on the GUI a three-dimensional image of the eye and IFS wherein the IFS is colored with a first color at points where the laser light will strike the fovea critical region, a second color where the laser light will strike the fovea caution region and a third color where the laser light will strike neither the fovea critical region or the fovea caution region.
Further objects, features and advantages of the invention will become apparent from the detailed description in conjunction with the following drawings.